Because of the growth of wireless communications, efforts have been made to increase the amount of wireless spectrum permitted to be used by networks such as wireless local area networks (WLANs). WLANs typically use spectrum in the unlicensed 2.4 GHz Industrial Services and Medical (ISM) band and the 5 GHz Unlicensed National Information Infrastructure (UNII) band. For example, in the United States the Federal Communications Commission (FCC) has permitted unlicensed systems to use portions of wireless spectrum that is licensed to television broadcasters. This licensed spectrum is known as the television white space band (TVWS) and is located in the very high frequency (VHF) and ultra-high frequency (UHF) bands. Wireless networks, such as WLANs, may benefit from the long range propagation and building penetration properties of VHF and UHF bands compared to the unlicensed spectrum bands. However, while use of the unlicensed bands is unrestricted for unlicensed devices, use of the licensed bands for unlicensed devices is subject to restrictions. For example, unlicensed devices may transmit in the TVWS only as long as they do not interfere with the licensed users of the TVWS spectrum such as television broadcasters and licensed wireless microphones.
Because of the requirements that use of restricted bands be noninterfering with other users, restricted band channels should generally only be used when necessary and not be used when other acceptable unrestricted band channels are available. Adherence to these requirements means that a wireless network that utilizes both restricted and unrestricted frequency bands is an environment where associations and re-associations occur on different channels with access points of the network on a frequent and regular basis. For example, a device using TVWS channels in a WLAN should check for availability of, for example, 2.4 GHz or 5 GHz channels in between sessions and change channels when available channels are found.
Channel scanning is generally performed by a device when the device wishes to associate with (e.g., become part of or join) a wireless network, switch channels in a wireless network or when a device wishes to re-associate with a network. The time it takes for a device to perform channel scanning, which may be up to two or more seconds, may be fairly significant in a wireless-networking environment where associations and re-associations occur frequently. Channel scanning also consumes resources of a device, requiring increased processing and power capability.